1. Field of the Invention
The present application relates to a communications terminal apparatus, and more particularly to a communications terminal apparatus that is capable of detecting various busy tones including ones out of standards.
2. Discussion of the Related Art
Communications terminal apparatuses, such as facsimile apparatuses, personal computers, and so forth, are required to have a function for detecting a busy tone to disconnect a telephone line. Specifically, when a facsimile apparatus, for example, initiates an automatic call to a destination facsimile apparatus which is then in busy status, a busy tone signal is transmitted by a telephone switching system, i.e. a private branch exchange (PBX), to which the initiating facsimile apparatus is coupled through a subscriber's line. The busy tone signal is transmitted to the initiating facsimile apparatus through a subscriber's line and contains a waveform having two alternate states which are a busy tone and off-tone states. Since the signal produces a tone in a busy tone state and no tone in an off-tone state, repeating the two states produce an intermittent buzzer, which is referred to as a busy tone, for informing a communications terminal apparatus and a user that a destination apparatus is in busy state.
When the initiating facsimile apparatus detects a busy tone, the telephone line which is then connected is preferred to be immediately disconnected, so that the subscriber's line is free to receive an incoming call and, accordingly, an improvement can be made on efficiency of telephone line engagement.
As another example, a telephone in an automatic answering and recording operation mode is needed to immediately disconnect a telephone line in a case that a calling party releases the line after completing his transmission of voice messages to the telephone. In this case, a busy tone may mistakenly be recorded as a noisy sound after the voice massages if the telephone does not disconnect the line relatively soon after the calling party finishes transmission of voice messages. The line disconnection at the telephone side can be performed with an assistance of a function for detecting a predetermined time period for an off-tone after the calling party finishes voice message transmission or for detecting a busy tone transmitted from a telephone switching system which detects a disconnection at the calling party side and generates a busy tone to a subscriber's line coupled to the telephone. The above-mentioned type of telephone is often incorporated in communications terminal apparatuses such as facsimile apparatuses, personal computers having a communications function, and so forth.
In the above-mentioned facsimile apparatus, for example, which detects a busy tone to disconnect the line, the busy tone detecting function is needed to be performed in a precise manner.
Generally, a busy tone is generated by a telephone switching system, to which a communications apparatus is coupled, and transmitted to the communications apparatus through a subscriber's line. When all the telephone switching system generates a busy tone that has a common characteristic, a communications terminal apparatus is capable of detecting such a busy tone having a common characteristic regardless of types of telephone switching systems.
In Japan, for example, a telephone switching system is required to generate a busy tone signal that has a waveform illustrated in FIG. 13 as a signal A. Such a busy tone signal can be understood as a signal made by modulating a signal having a waveform of 400 Hz.+-.19 Hz illustrated in FIG. 13 as a signal B with a modulation signal having an on and off ratio of 50%.+-.10% and a cycle of 60 Hz.+-.20% illustrated in FIG. 13 as a signal C. However, telephone switching systems practically generate a signal having the shape of signal A of FIG. 13 by switching the signal B of FIG. 13, on and off, at predetermined intervals. Therefore, a busy tone signal can be defined by several values such as switching cycles, on-time and off-time periods, and so forth. These values are referred to as cadence characteristics.
From the above, a busy tone can properly be detected by previously knowing several characteristics of an actual busy tone signal on a telephone line, such as a frequency, and tone and off-tone state time periods.
There are countries where facsimile apparatuses are required to include a function for detecting a busy tone in an automatic call initiation operation. In these countries, the facsimile apparatuses have parameters which correspond to characteristics of a busy tone so as to detect a busy tone according to the requirements. Further, in facsimile apparatuses having an automatic answering and recording function, it is possible to terminate a recording operation by detecting a busy tone using the parameters, when a calling party finishes transmission of voice messages.
Despite the above-mentioned requirements, telephone switching systems that are aged and therefore transmit a busy is tone signal out of standards are still in operation in some countries. In this case, the characteristics of busy tone varies between telephone switching systems. This causes problems in that parameters provided to facsimile apparatuses may not fit to the busy tone characteristics of the telephone switching systems in some cases. As a result, the facsimile apparatuses may fail to detect a busy tone and to disconnect the telephone line while the line of the counter party of communications is disconnected.
When failing in the busy tone detection, the problem may not result in a capital error because in the automatic answering and recording function the facsimile apparatuses normally has a function for automatically disconnecting the telephone line in a predetermined time period which safeguards an event of failure in busy tone detection. However, the busy tone detection failure may cause a serious problem during the automatic answering and recording operation. In this case, the facsimile apparatuses automatically record the busy tone as a noisy sound as long as the line is connected. This results in a waste of recording medium and a reduction of telephone line engagement efficiency.
Adjusting the parameters for a busy tone at each of the facsimile apparatuses by service personnel may require a considerable amount of work force and cost since most countries have a large number of facsimile apparatus installations.
This problem of a busy tone is not limited to the telephone switching systems that are for subscriber lines. In a case of the telephone switching systems that are for extension lines, a similar problem occurs.
The present problem is that there is no communications terminal apparatus capable of detecting various busy tones including ones out of standards.